How can I generate this plot?

Question

Monique Embury 2020-2-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/504092-how-can-i-generate-this-plot

评论： Adam Danz 2020-2-25

Hi,

I am trying to generate similar looking plots to the one attached. With this, do you know what kind of plot this is? And how to get the black bars showing where the orifice opening is?

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Monique Embury 2020-2-25

在 MATLAB Online 中打开

Hi Adam,

Going back to the code I shared with you on another post, I am trying to plot the heat map with the quiver function overlaid. I am a bit confused on how to set up imagesc() after reading through the different tutorials. Could you help?

function [x,y,u_avg,v_avg,CHC_tot] = piv_averages(prefix,suffix,Nstart,Nfinish,interp)
% This program reads in a series of instantaneous PIV vector fields from
% Insight and averages them.  The user has the option of excluding
% interpolated vectors, which have CHC > 1.  (interp = 0 means do not 
% interpolate, while interp = 1 means interpolate).
% Create file name for each image
c_exit=2.776; %speed of sound
x0=1040; %origin of the jet in pixels  
y0=53.8; %origin of the jetin pixels
D=923.71; %diameter of jet exit in pixels 
v_shift=0;
for i = Nstart:Nfinish
    Nstring = int2str(i);       % Convert iteration number to a character string
    if i < 10
        filename_inst = strcat(prefix,'0000',Nstring,suffix);
    elseif i < 100
        filename_inst = strcat(prefix,'000',Nstring,suffix);
    elseif i < 1000
        filename_inst = strcat(prefix,'00',Nstring,suffix);
    elseif i < 10000
        filename_inst = strcat(prefix,'0',Nstring,suffix);
    else
        filename_inst = strcat(prefix,Nstring,suffix);
    end
    % Read file name
    A_inst = csvread(filename_inst,1,0);
    x = A_inst(:,1)-32;             % x-position (mm)
    y = A_inst(:,2)-198.2;             % y-position (mm)
    u = A_inst(:,3);             % x-velocity (m/s)
    v = A_inst(:,4);             % y-velocity (m/s)
    chc = A_inst(:,5);           % number of good vectors at this location
    N = size(x,1);               % Length of entire vector array
    
    % Initialize output variables if this is the first file
    if i == Nstart
        u_tot = zeros(N,1);
        v_tot = zeros(N,1);
        CHC_tot = zeros(N,1);
    end
     
    for j = 1:N
        if interp == 0
            if chc(j,1) == 1
                u_tot(j,1) = u_tot(j,1) + u(j,1);
                v_tot(j,1) = v_tot(j,1) + v(j,1);
                CHC_tot(j,1) = CHC_tot(j,1) + 1;
            end
        elseif interp == 1
            if chc(j,1) > 0
                u_tot(j,1) = u_tot(j,1) + u(j,1);
                v_tot(j,1) = v_tot(j,1) + v(j,1);
                CHC_tot(j,1) = CHC_tot(j,1) + 1;
            end
        end
    end
end
for j = 1:N
    u_avg(j,1) = u_tot(j,1)/CHC_tot(j,1);
    v_avg(j,1) = v_tot(j,1)/CHC_tot(j,1);
end
% define orifice opening in pixels 
orificepl=linspace(0, x0-(D/2));
orificepr=linspace(x0+(D/2), 2016);
yorifice=2016*ones(size(orificepl));
% define orifice opening in mm
orificeml=linspace(0, (x0-(D/2))/48.11);
orificemr=linspace((x0+(D/2))/48.11, 2016/48.11);
% define orifice opening non-dimensional
orificendl=(orificepl-x0)/D;
orificendr=(orificepr-x0)/D;
% Set origin to jet exit centerline
x_c = x - (x0);
y_c = y - y0;
% Shift by convective velocity
v = v - v_shift;
% Nondimensionalize variables
x_non = x_c/D;          % Nondimensionalize using jet diameter
y_non = y_c/D;          % Nondimensionalize using jet diameter
u_non = u_avg/c_exit;       % Nondimensionalize using sonic speed
v_non = v_avg/c_exit;       % Nondimensionalize using sonic speed
% Plot nondimensional vector field
figure(2)
quiver(x_non,y_non,u_non,v_non,4)
line(orificendl,yorifice/1008, 'linewidth', 4, 'color', 'k')
line(orificendr,yorifice/1008, 'linewidth', 4, 'color', 'k')
axis([-1 1 0 2])
xticks([-1 0 1])
yticks([0 1 2])
colormap(jet)
set(gca,'YtickLabel',2:-1:0)
set(gca,'XAxisLocation','top','YAxisLocation','left');
xlabel('z/D')
ylabel('x/D')
title('Nondimensional velocity field')
camroll(90)

Adam Danz 2020-2-25

What defines the color mapping? Another way of asking that, what defines the colobar scale?

Is it the magnitude of the quiver vectors? What defines positive and negatve values? If pos & neg values are defined by the direciton of the quiver vectors, which directions define pos and neg?

Monique Embury 2020-2-25

I would say that it is defined by the magnitude. Where positive is defined from moving left to right and negitive by right to left.

Without applying the camera roll as I did in the figure, the positive would be from top to bottom and negative would be bottom to top.

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Answer 1

Adam Danz 2020-2-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/504092-how-can-i-generate-this-plot#answer_417328

编辑：Adam Danz 2020-2-25

在 MATLAB Online 中打开

The quiver arrows all have fairly small magnitudes which makes it difficult to see the arrows but you can reproduce the figure and zoom in inspect parts of the image.

See inline comments for details.

% Load the data
data = load('average_vels.mat');
% Extract quiver variable for readability
x = data.output_avg(:,1); 
y = data.output_avg(:,2); 
u = data.output_avg(:,3); 
v = data.output_avg(:,4); 
% Compute signed magnitude of the quiver vectors where 
% positive magnitudes point upward and neg mags point downward
z = hypot(u,v) .* sign(v);
% Reshape the z vector into a matrix where 
% zMat(i,j) is the value at x=xVec(i) and y=yVec(j).
[xVec,~, zRow] = unique(x); 
[yVec,~, zCol] = unique(y);
zMat = nan([numel(xVec),numel(yVec)]); 
zIdx = sub2ind(size(zMat),zCol, zRow); 
zMat(zIdx) = z;
% Plot the "heatmap" first
clf()
imagesc(xVec, yVec, zMat)
set(gca, 'YDir', 'Normal') 
cbh = colorbar();
ylabel(cbh, 'Vector magnitude (positive is upward')
axis equal
% add the quiver data
hold on
quiver(x,y,u,v)

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Monique Embury 2020-2-25

Thank you for the tip!

Adam Danz 2020-2-25

在 MATLAB Online 中打开

Monique, one last thought. If you want white to represent 0 velocity and two other colors (red & blue in this example) to represent upward and downward quiver vectors, you can apply this colormap at the end of the code.

cmap = [linspace(0,1,128)'*[1,1], ones(128,1)]; % The blue range
cmap = [cmap; rot90(cmap,2)];                   % add the red range
set(gca, 'Colormap', cmap)                      % set the colormap
caxis(max(abs(cbh.Limits)) * [-1,1]);  %center the color range so white is in the middle